Aspects of the present invention relate generally to linear actuators, and more particularly to a low backlash linear actuator exhibiting fast response and minimal overshoot.
Conventional mechanical and electromechanical systems providing linear motion for positioning structural components typically employ actuator mechanisms which require that the moving, or translated, component always approach a desired or target position from the same direction. Such unidirectional approach strategies attempt to optimize accuracy by minimizing positional errors contributed or exacerbated by rotational backlash in the drive mechanism. In this context, the term xe2x80x9cbacklashxe2x80x9d generally refers to inaccuracies (e.g., play, or looseness) in the connections between the drive components which require that a motor drive shaft, a coupling mechanism, or both must rotate through some initial angular displacement before any motion is coupled to the translated component. As is generally known, the unidirectional approach to alleviating backlash often requires that the actuator translate the component linearly beyond a desired target position; the actuator may then be reversed such that the translated component approaches the target position from the xe2x80x9ccorrectxe2x80x9d or selected direction. In addition to the foregoing inefficiency, such traditional systems are generally characterized by slow response times and inaccurate control loops.
Some systems attempting to avoid the unidirectional approach strategy utilize a high resolution piezoelectric actuator operably coupled to a feedback loop. In such arrangements, the feedback loop is necessary as a consequence of the significant hysteresis characteristic of piezoelectric actuators. While nominally overcoming some of the efficiency problems associated with approaching the target position from a single direction, disadvantages of such a piezoelectric actuator implementation include, among other things, significantly limited overall travel range (e.g., travel is usually less than about 60 xcexcm).
Embodiments of the present invention overcome the above-mentioned and various other shortcomings of conventional implementations, providing a high-precision, low backlash linear actuator exhibiting minimal positional repeatability error regardless of directional approach to the target position.
In accordance with one embodiment, for example, an actuator drive mechanism may employ a bellows coupling operative to transmit rotational motion from a motor to a drive spindle. Rotation of the drive spindle may cause linear translation thereof in an axial direction.
Specifically, in some embodiments, a drive mechanism comprises: a motor; a drive spindle; and a bellows coupling configured and operative to transmit rotational motion from the motor to the drive spindle allowing rotation of the drive spindle about an axis; wherein the rotation of the drive spindle causes the drive spindle to translate in an axial direction.
The bellows coupling may comprise a bellows having a first end operably coupled to the motor and a second end operably coupled to the drive spindle. As set forth in detail below, the first end of the bellows may generally be fixed in an axial position relative to the motor; the second end of the bellows translates with the drive spindle in the axial direction.
In accordance with some embodiments, the drive spindle comprises a threaded section threadably engaged with a cooperating structure fixed in an axial position relative to the motor. The cooperating structure may be incorporated in or fixedly attached to a housing.
The motor generally comprises a rotatable coupling mechanism operative to transmit rotational motion to the bellows; the first end of the bellows generally comprises means for preventing annular slipping of the bellows relative to the rotatable coupling mechanism. Similarly, the second end of the bellows generally comprises means for preventing annular slipping of the drive spindle relative to the bellows. Accordingly, torque may be efficiently transferred to the bellows from the motor, and from the bellows to the drive spindle. In some implementations, the means for preventing annular slipping comprises a set screw; other such means and mechanisms for preventing annular slipping are contemplated.
In accordance with some exemplary embodiments, a linear actuator comprises: a housing; a motor fixedly attached to the housing; a drive spindle; and a bellows coupling configured and operative to transmit rotational motion from the motor to the drive spindle allowing rotation of the drive spindle about an axis; wherein the housing comprises a structural component fixed in an axial position relative to the motor and cooperating with the drive spindle such that the rotation of the drive spindle causes the drive spindle to translate in an axial direction.
As with the implementations of a drive mechanism noted above, the bellows coupling generally comprises a bellows having a first end operably coupled to the motor and a second end operably coupled to the drive spindle. The first end of the bellows is fixed in an axial position relative to the motor. The second end of the bellows translates with the drive spindle in the axial direction.
In the exemplary embodiments, the drive spindle comprises a threaded section threadably engaged with the structural component, which may be embodied in or comprise a threaded nut, for example, or a similar component integrated or associated with the housing.
The motor comprises a rotatable coupling mechanism operative to transmit rotational motion to the bellows; the first end of the bellows comprises means for preventing annular slipping of the bellows relative to the rotatable coupling mechanism. Similarly, the second end of the bellows comprises means for preventing annular slipping of the drive spindle relative to the bellows. As noted above, torque may be efficiently transferred to the bellows from the motor, and from the bellows to the drive spindle. In some implementations, the means for preventing annular slipping comprises a set screw; other such means and mechanisms for preventing annular slipping are contemplated.
The foregoing and other aspects of various embodiments of the present invention will be apparent through examination of the following detailed description thereof in conjunction with the accompanying drawings.